Xechalcogen aerogen bond. Effect of substituents and size of chalcogen atom.

The aerogen bond between the Xe and chalcogen atoms in complexes pairing XeOF2 with R1YR2 is examined by ab initio calculations for Y = O, S, and Se. In addition to HYH, one or both H atoms are changed to F or methyl groups. The interaction energies are strong, varying between 21 and 54 kJ mol-1. The aerogen bond is composed of roughly half electrostatic attraction, with lesser contributions due to polarization and dispersion. Replacement of H by electron-withdrawing F on the base weakens the interaction, while electron releasing Me substituents have the opposite effect. Whereas the aerogen bonds are stronger for O than for S or Se for HYH, HYF, and MeYH, it is the heavier chalcogen atoms that form the stronger dimers for MeOF and MeOMe. These trends cannot be fully explained by molecular electrostatic potentials or by measures of charge transfer, nor are they entirely consistent with electron density topology.